A washing machine is a domestic appliance for cleaning clothes, linens, and other laundry. A washing machine may include a tub and a drum positioned in the tub that is sized to receive laundry for cleaning. The washing machine may include an electric motor that causes the drum to rotate relative to the tub during a washing operation. In some washing machines, the electric motor may be connected to the drum via a transmission system including, for example, belts and pulleys or gears. The electric motor may also be connected to the drum via a drive shaft. Washing machines including the latter type of electric motor are often referred to as “direct drive” washing machines.
In horizontal washing machines, the washing cycle commonly includes several starting and stopping phases. More particularly, the drum starts to rotate in one direction in a starting phase. Once the drum has reached a desired tumbling speed, the drum enters a tumbling phase and rotates substantially at the desired tumbling speed. After the tumbling phase is completed, the washing cycle begins a stopping phase, and the speed of the drum decreases until the drum stops moving. The drum remains stationary for a preset period of time, until a new starting phase begins and the drum begins to rotate again, sometimes in the other rotational direction. Thus, in the entire washing cycle, the drum may be started from a stopped position many times.
Accordingly, starting the drum from a stopped position may require starting the electric motor from a stopped position. Additionally, the drum may be filled with laundry and water, meaning high motor torque may be required to start the rotation. For permanent magnet synchronous electric motors to deliver the required torque on start, the initial position of the rotor of the motor must be determined with reasonable accuracy. For motors with multiple electrical poles, the electrical position of the rotor may be determined rather than the physical rotor position.